1. Field of the Invention
The present invention relates to a radiation-emitting optical component, in particular a radiation-emitting optical component having a radiation-emitting semiconductor component, which is encapsulated by a transparent material.
2. Background of the Invention
Known radiation-emitting semiconductor components have a layer structure which contains an active layer which, in operation, emits radiation with a certain spectral distribution. Electrical contacts are used to apply a current to the layer structure.
It is customary to embed radiation-emitting semiconductor components of this type in a casting material which is transparent at the relevant useful wavelengths. However, particularly in the case of blue and white light-emitting diodes, the problem arises that after a prolonged operating time, the light-emitting diodes display a considerable decrease in brightness.
The light loss is caused by ageing of the casting resin, which is subject to brown discoloration after a certain operating time of the light-emitting diode. This effect considerable shortens the service life of blue and white light-emitting diodes.
It is in principle possible to slow the ageing of the casting resin. For example, unpublished tests carried out by the applicant have established that adding a stabilizer to the epoxy resins used as casting material delays the brown discoloration. The service life of blue and white light-emitting diodes can as a result be approximately doubled by the addition of a stabilizer.
An alternative approach consists in replacing the epoxy resins of the casting material with more stable polymers. In this context, silicons, whose polymer network is composed predominantly of the very stable Si—O bonds, are particularly recommended. However, silicons entail a range of other disadvantages. They have poor adhesion and a very high expansion coefficient, which lead to considerable stresses during heating and cooling.
On account of the poor adhesion, foreign substances can easily penetrate at boundary surfaces, leading to reliability problems. Moreover, silicons have a soft consistency, which can lead to problems in what are known as pick-and-place processes. Finally, silicons have a lower refractive index than hydrocarbon-based polymers, which leads to a lower light yield when they are used in light-emitting diodes.